Prior to the liquefaction of a hydrocarbon-rich gas stream, those components which freeze-out during the liquefaction process and therefore lead to an alteration of the process must be removed, on principle, from the gas stream to be liquefied. In particular the component benzene must be standardised to contents of &lt;1 ppm in the liquefied hydrocarbon-rich stream.
The separation of these undesirable components, namely the aromatic and the heavy hydrocarbons, can, on principle, be undertaken in two different ways. In the event that the hydrocarbon-rich gas stream to be liquefied has a comparatively high proportion of heavy hydrocarbons, it is, prior to the actual liquefaction process, fractionated into one fraction consisting of heavy and aromatic hydrocarbons, and another fraction consisting of lighter hydrocarbons. Subsequently only the fraction consisting of lighter hydrocarbons is subjected to liquefaction. This method however has the disadvantage that it is firstly too expensive and secondly requires an independent process unit, i.e. with its own cooling and heating cycles.
In the event that the hydrocarbon-rich gas stream has lower proportions of aromatic and heavy hydrocarbons, it is recommended that separation of the heavy and the aromatic hydrocarbons be by way of adsorption. To achieve this, the adsorber or adsorbers used for the requisite drying and, if required, removal of carbon dioxide from the hydrocarbon-rich gas stream are dimensioned to be correspondingly larger or, in addition, equipped with suitable adsorbents which are capable of adsorbing the aromatic and the heavy hydrocarbons from the gas stream to be liquefied. A disadvantage of this method is however that, on the one hand, the adsorber or adsorbers used would have to be dimensioned larger and, on the other hand, that the gas recovered during the regeneration of the charged adsorbers is loaded, to a large extent, with heavy and aromatic hydrocarbons.